1. Field of the Invention
The present invention relates to an optical disc apparatus for reading and writing data from and onto an optical disc on which a guide groove is formed wobblingly and provided with address information being modified around a predetermined frequency in advance, and in particular, relates to an optical disc apparatus which controls a spindle motor by detecting a wobble signal obtained from the above address information, and a spindle motor controller apparatus thereof.
2. Description of Prior Art
Conventionally, for a purpose of recording data upon an optical disc with high accuracy by an optical disc apparatus, a spindle motor is controlled in the revolution number and the phase thereof. On the surface of the optical disc being developed for the purpose of simplification of the control of the spindle motor, address information being modified around a predetermined frequency is provided in advance on a guide groove which is formed wobblingly, i.e., with a so-called wobbling groove method. With this optical disc, there is no necessity of providing a so-called ID pits on it, therefore the guide groove is continuous. The optical disc apparatus detects a wobble signal from this guide groove so as to acknowledge the address information, and also detects the frequency and the phase of the wobble signal, thereby performing a PLL control of the spindle motor so as to obtain the frequency at a desired one.
Also, when controlling the revolution or rotation of the above-mentioned spindle motor, it is controlled by generating a clock signal for use of rotation control by means of an oscillator of PWM (a pulse wave modulation).
The clock frequency is determined at the upper limit by a frequency band of the controller circuit and at the lower limit by control characteristic of revolution number, for example, approximately 100 KHZ. If the frequency band is set in the high frequency side, noise signal is generated on the reproducing signal since the clock frequency is in a vicinity of the frequency band of the controller circuit.
According to this conventional art, since the guide groove being provided on the optical disc is continuous, detection of the wobble signal is possible under the condition that the revolution number of the spindle motor cannot be identified, as well as the PLL control of the spindle motor. It is of course, but in a case where no wobble signal can obtained, the recording cannot be obtained because of ambiguity of the address.
Further, at the present, an optical disc is proposed for the purpose of high density thereof, which is different from the format mentioned above. On this optical disc, there are provided a guide groove wobbling at a predetermined frequency and an ID pit indicating an ID of a sector, which is positioned at a cutting portion of the guide groove. The wobble signal obtained from this optical disc, since it is detected from the very small or minute wobbling guide groove, although it is determined at a constant or predetermined value, is small in the amplitude. Therefore, it is extracted or sampled by means of a low-pass filter to be amplified thereafter.
On a while, the clock signal for rotation control, which is outputted from the above PMW oscillator is used as the rotation control signal for the spindle motor, and it is large enough in the amplitude of current, therefore there is a problem that it generates noises therefrom. In particular, in a case where the frequency of the clock for rotation control which is outputted from the above PWM oscillator is set a frequency in the vicinity of an area of wide capture fluctuation of the wobble signal, it gives a harmful or ill influence upon the detection of the small or minute wobble signal, thereby generating a beat on the wobble signal, i.e., there occur difficulties in a preferable detection of the wobble signal as well as in an operation control of the spindle motor being controlled thereby.
Accordingly, an object of the present invention is to provide an optical disc apparatus, with which an external disturbance upon the wobble signal or the like can be reduced, thereby achieving a stabilization of the disc apparatus.
According to the present invention, for achieving the object mentioned above, there is provided an optical disc apparatus for recording into or reproducing from an optical disc, on which a guide groove wobbling at a predetermined frequency and ID pits indicating IDS of sectors at cutting portions of said guide groove are provided, comprising:
a driver motor for rotating said optical disc;
a signal extracting circuit for extracting a control information from said wobbling guide groove;
a wobble detection circuit for extracting a wobble signal from the control information extracted by said signal extracting circuit;
a driver motor controller circuit for controlling rotation number of said driver motor; and
a clock oscillator circuit for outputting a clock for use of rotation control of said driver motor, wherein a frequency of said clock for use of rotation control is set at a frequency to be different from the frequency of said wobble signal.
Preferably, according to the present invention, there is provided the optical disc apparatus as described in the above, wherein said clock oscillator circuit is a pulse wave modulation oscillator, and the frequency of the clock for use of rotation control is set outside the frequencies in an area of wide capture fluctuation of the wobble signal.
Further preferably, according to the present invention, there is provided the optical disc apparatus as described in the above, wherein the area of wide capture fluctuation is in xc2x150% of the frequency of the wobble signal. Further, wherein the frequency of the clock for use of rotation control is set to be higher than the frequency of the wobble signal.